(1) Field of the Invention
The present invention relates to a system in which encryption authentication communication is performed between a plurality of devices.
(2) Description of the Related Art
Content distribution services that distribute various music and movies using packaged media, the Internet or broadcasting have become prevalent in recent years. Such services require content protection techniques that reflect the wishes of the protector of copyright of the content. The protector may wish, for example, to charge for the content distribution service, and to limit the content to individual usage in homes of users who have a content distribution contract. Alternatively, the protector may wish to prohibit transmission of the content over the Internet, since the Internet can be accessed by numerous unspecified users.
DTCP (Digital Transmission Content Protection) is one system that offers a content protection technique for realizing the wishes of the content copyright protector. In DTCP, digital content is distributed via a bus specified by IEEE1394, which is one specification for a high-speed serial bus. DTCP is described in detail in Document 1.
In DTCP, encryption authentication communication is performed between mutually connected devices that comply to DTCP specifications, under the management of a manager called a DTLA (Digital Transmission Licensing Administrator, LLC). The encryption authentication works as follows.
(1) A transmission apparatus and a reception apparatus both have an individual secret key distributed by the DTLA based on a contract with the DTLA. Note that devices to which the secret key is distributed use a prescribed secret key management implementation method. Furthermore, transmission of content over the Internet is prohibited by the DTCP contract.
(2) The transmission apparatus and the reception apparatus perform mutual authentication using the secret key. Furthermore, the transmission apparatus encrypts content that requires protection, using a key that has been shared in authentication, and transmits the encrypted content to the reception apparatus.
(3) The transmission apparatus gives each of a maximum of 63 reception devices a key for decrypting the content. Individual usage of content can be easily realized by AVC command restrictions and device number restrictions specified by IEEE1394.
The following describes an outline of an authentication system that uses Kerberos. Note that Kerberos is described in detail in Document 2.
In Kerberos, legal devices are registered in advance in a Kerberos server. As one example, in order to use content, a device first accesses the Kerberos server, receives a first authentication from the Kerberos server based on registered information, and obtains a ticket (initial ticket) that is valid for that day from the Kerberos server. Next, the device accesses a server that provides a service, presents the initial ticket received from the Kerberos server, receives a second authentication from the server, and then uses the content.
In this way, in Kerberos, a registered device is able to use any service freely within the determined validity period by being authenticated twice.
However, neither of the above-described methods enable differentiation between home devices and external devices, and therefore do not enable limitation of individual usage inside the home of a user who has a content distribution contact.
<Document 1>
5C Digital Transmission Content Protection White Paper, Revision 1.0, Jul. 14, 1998
<Document 2>
Tung, Brian KERBEROS Network Ninsho System (KERBEROS: A Network Authentication System), trans. Kuwamura, Jun, Pearson Publishing, 1999